Conventionally, what is known as a document reader that reads both sides of a document where images are formed on the two sides is: a device that includes a document conveyance device having a reversing mechanism that turns a document upside down, and which conveys a document to a reading unit and thereby reads one side of the document and then turns over the document by using the reversing mechanism and conveys again the document to the reading unit to read the other side of the document; and a device that includes a first reading unit for reading one side of a document and a second reading unit for reading the other side of the document, and which reads the document by using the first and second reading units.
The latter document reader are disclosed in Patent Documents 1, 2, and 3, for example. In the case of this device, in a main body of the document reader, a first reading unit of a reduction optical system is provided; in a document conveyance device that is so provided as to be freely opened and closed in the main body of the document reader, a second reading unit of the reduction optical system is provided. The second reading unit provided in the document conveyance device is disposed on a downstream side of the first reading unit, and is provided on an inner side of a document conveyance path that is formed into a U-shape.
Both the first and second reading units include a light source that emits light to a document via a contact glass surface; a plurality of mirrors that guide the light reflected from the document to a predetermined direction; a lens that converges the reflected light which is guided by a plurality of the mirrors where the light is reflected a plurality of times; and a photoelectric conversion element (COD) that carries out photoelectric conversion of the light converged by the lens. The light that is emitted from the light source to the surface of the document is reflected by a plurality of mirrors, and is read by the photoelectric conversion element via the lens. Image information of the document that is read by the photoelectric conversion element is transmitted as electric signals to an image processing unit. After image processing is performed, the signals are output.